In recent years, wind and flood disasters occur frequently worldwide. The disasters usually swell rivers and creeks, making the foundations of bridge piers be scoured severely and thus exposing the piles of the piers. Consequently, the lateral resistance of a bridge is deficient, which results in tilt or break of the bridge. If the floods are heavy, the piers will be broken directly, and hence collapsing the bridge in a sudden and endangering traffic safety. The situation not only results in traffic breakdown, but also brings a great loss of civilian lives, public properties, and local constructions in a short time. Presently, in order to understand the scouring condition of the bed around a pier and thereby launching immediate early warnings, a monitoring system is developed. Accordingly, the traffic safety can be assured; the secondary injuries owing to bridge break can be avoided; and the lifetime of the bridges can be extended by timely reinforcement and repair. Furthermore, the monitoring data can be recorded in the long term for establishing complete database of pier scouring, which can be used for pier protection and bed remediation in the future.
Currently, the mostly adopted monitoring methods among many related techniques for monitoring pier scouring are described as follows.
Ground-penetrating radar method: This is a non-destructive inspecting technique, which uses high-frequency electromagnetic wave source to transmit radar wave for penetrating various material layers and deducing the elevation variations of the bed. The advantage of the present method is that the elevation variation of the bed can be recorded continuously; while the drawbacks thereof are that the operation is time-consuming and that the professional training is required for operation.
Numbered bricks method: This method uses a brick array composed of a plurality of bricks with fixed size. Each of the bricks is numbered sequentially and marked, and is buried under the bed upstream to the bridge pier. When the floods come, the elevation variations of the bed can be approximated by measuring the displacement and amount of bricks scoured from their original locations. The drawbacks of the present method include the need of digging out the bed and single use only. Besides, only the scoured depth can be measured while the silt depth is not available.
Sliding magnetic collar method: A hollow sliding shaft with an external collar is disposed on the surface of the pier post. When the bed is scoured, the collar will move downward, providing the scouring depth of the specific location. A magnetic sensor is disposed inside the sliding shaft. The magnetic sensor can move synchronously to the external collar and transmit the moving signal outside by using a circuit. The drawback of the present method is that only the scoured depth can be recorded while the silt depth is not available.
Water-level identification using outdoor monitoring lenses: This method extracts the image of the water level under test using an image extraction apparatus. The extracted image is conducted by a series of image process to give the elevation of the water surface. However, the present method cannot monitor pier scouring.
Self-moving lens monitoring method: This method is the Taiwan invention application number 098131157 by the present applicants. According to the method, a hollow container is buried in the bed beside the pier and fixed on the pier. The container includes a photographing apparatus disposed on a carrier for monitoring. A motor is used for controlling vertical movement of the carrier for monitoring the scouring condition of the sand surface. When the sand surface is raised by silting or lowered by scouring, the real-time image identification system can be used for tracking the sand surface. Thereby, both silting and scouring can be detected. The drawbacks of the method include huge power consumption used for controlling the movement of the carrier. In addition, because data are transmitted wirelessly, the transmission quality tends to be interfered by the motor.
Gravity-type scour measurement apparatus: When the sand surface is lowered by scouring, the detector will also sink lower owing to the gravity effect. Thereby the scouring depth can be given by reading the lowered height. The drawback of the apparatus is that only scouring can be detected. Silting cannot be measured.
Radio-transmitter-type scour monitoring system for soil layers: Multiple radio transmitters are buried in the soil layers. When the sand surface is scoured to a certain depth, the radio transmitter will be move or vibrated. Thereby, the scoring condition of the sand surface can be detected. The system's drawback is that only scouring can be detected. Silting cannot be measured.
Optical-fiber sensing system: This is a measurement system using optical-fiber gratings for monitoring. Because a medium attached to the optical fiber changes the internal refractivity of the optical fiber and shifts the wavelength of the internal light, the depth of the medium can be located and deduced. The drawback of the system is that the fragile optical fiber has to be attached directly to water or sand surface, and hence the optical fiber tends to be damaged.
According to the monitoring methods mostly adopted currently as described above, it is known that how to monitor the scouring condition of the bed around a pier in a better method for extending the lifetime of a bridge is a major subject at present.
Accordingly, the present invention provides a multi-lens monitoring system for bed elevation around a pier, which can solve the drawbacks according to the prior art and can real-timely monitor the elevation variations of the bed around the pier.